In vivo NMR T2 relaxation of experimental brain tumors in the cat: a multiparameter tissue characterization.

Experimental gliomas (F98) were inoculated in cat brain for the systematic study of their in vivo T₂ relaxation time behavior. With a CPMG multi-echo imaging sequence, a train of 16 echoes was evaluated to obtain the transverse relaxation time and the magnetization M(0) at time T = 0. The magnetization decay curves were analyzed for biexponentiality. All tissues showed monoexponential T₂, only that of the ventricular fluid and part of the vital tumor tissue were biexponential. Based on these NMR relaxation parameters the tissues were characterized, their correct assignment being assured by comparison with histological slices. T₂ of normal grey and white matter was 74 ± 6 and 72 ± 6 msec, respectively. These two tissue types were distinguished through M(0) which for white matter was only 0.88 of the intensity of grey matter in full agreement with water content, determined from tissue specimens. At the time of maximal tumor growth and edema spread a tissue differentiation was possible in NMR relaxation parameter images. Separation of the three tissue groups of normal tissue, tumor and edema was based on T₂ with T_2(normal) < T_2(tumor) < T_2(edema). Using M(0) as a second parameter the differentiation was supported, in particular between white matter and tumor or edema. Animals were studied at 1–4 wk after tumor implantation to study tumor development. The magnetization M(0) of both tumor and peritumoral edema went through a maximum between the second and third week of tumor growth. T₂ of edema was maximal at the same time with 133 ± 4 msec, while the relaxation time of tumor continued to increase during the whole growth period, reaching values of 114 ± 12 msec at the fourth week. Thus, a complete characterization of pathological tissues with NMR relaxometry must include a detailed study of the developmental changes of these tissues to assure correct experimental conditions for the goal of optimal contrast between normal and pathological regions in the NMR images.     

Applications of high-intensity focused ultrasound in medicine: Spotlight on neurological applications

High-intensity focused ultrasound (HIFU) has the potential to become a modality of treatment for a wide range of clinical conditions. HIFU enables non-invasive, selective ablation of tissues including tumors and punctured vessels. Another promising area of research within the field of therapeutic ultrasound is the application of HIFU to treat neurological disorders by selectively targeting the brain, spinal cord, or nerves. This paper provides an overview of the current applications of focused ultrasound in medicine with an emphasis on its use in the fields of neurology and neurosurgery.     

脑功能核磁共振成像在精神疾病中的应用

主要介绍了几种脑功能核磁共振成像方法以及在精神疾病中的研究情况.血氧水平依赖fMRI (BOLD-fMRI)是目前应用最广泛的fMRI技术,可利用神经激活后对局部血流的影响,间接显示神经活动.灌注加权成像是直接测定脑血流的fMRI技术,但由于它的时间分辨率比较低,对快速的脑功能难以进行研究.扩散加权象目前主要用于脑缺血的早期诊断,利用该技术也可示踪神经通路.化学位移成像能够检测局部组织代谢产物的含量,可反映不同脑区能量和物质代谢的状况,也是一种脑功能的研究手段.尽管这些技术在神经、心理学领域已经取得非常可喜的进展,目前fMRI在精神疾病方面的工作较少,相信随着技术的改进,fMRI必将在精神疾病方面大显身手.     

Microdialysate analysis of monoamine neurotransmitters—A versatile and sensitive LC–MS/MS method

We have developed and validated a sensitive method for the simultaneous determination of some monoamine neurotransmitters like dopamine (DA), norepinephrine (NE) and serotonin (5-HT) in rat brain microdialysate using high-performance liquid chromatography coupled to tandem mass spectrometry (LC/MS/MS). Sensitivity enhancement has been achieved by amine derivatization with the reagent (5-N-succinimidoxy-5-oxopentyl)triphenylphosphonium bromide (SPTPP) under mild conditions. The use of the selected reaction monitoring (SRM) mode has allowed detection of the analytes at a concentration of 30 pM (lower limit of quantification, LLOQ, signal-to-noise ratio higher than 5) with an accuracy of ≤3.80% and a precision of ±7.39 (%CV) for all neurotransmitters. Derivatization improves resolution and chromatographic retention times (3 min) by lipophilization. Linearity has been good (R > 0.99) over a large concentration range (30–50,000 pM). The intra and inter-batch accuracy and precision were not greater than 4.8% and 6.4%, respectively. Therefore, the method was successfully applied for monitoring the concentration changes of neurotransmitters in microdialysis samples deriving from striatum rat brain region after amphetamine administration (3 mg kg⁻¹, i.p.).     

Phase-difference and spectroscopic imaging for monitoring of human brain temperature during cooling

Decrease of the human brain temperature was induced by intranasal cooling. The main purpose of this study was to compare the two magnetic resonance methods for monitoring brain temperature changes during cooling: phase-difference and magnetic resonance spectroscopic imaging (MRSI) with high spatial resolution. Ten healthy volunteers were measured. Selective brain cooling was performed through nasal cavities using saline-cooled balloon catheters. MRSI was based on a radiofrequency spoiled gradient echo sequence. The spectral information was encoded by incrementing the echo time of the subsequent eight image records. Reconstructed voxel size was 1×1×5 mm³. Relative brain temperature was computed from the positions of water spectral lines. Phase maps were obtained from the first image record of the MRSI sequence. Mild hypothermia was achieved in 15–20 min. Mean brain temperature reduction varied in the interval <−3.0; − 0.6>°C and <−2.7; − 0.7>°C as measured by the MRSI and phase-difference methods, respectively. Very good correlation was found in all locations between the temperatures measured by both techniques except in the frontal lobe. Measurements in the transversal slices were more robust to the movement artifacts than those in the sagittal planes. Good agreement was found between the MRSI and phase-difference techniques.